This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application entitled DEVICE AND METHOD FOR DIVERSITY COMBINING SIGNALS ON COMMON CHANNEL IN CDMA COMMUNICATION SYSTEM earlier filed in the Korean Industrial Property Office on Aug. 5, 1998, and there duly assigned Serial No. 98-32353.
1. Field of the Invention
The present invention relates to a message communication device and method for a mobile communication system, and, more particularly, to a device and method for transmitting and receiving messages on a common channel in a Code Division Multiple Access (CDMA) communication system.
2. Description of the Related Art
To transmit and receive data between a base station and a mobile station before a voice call is set up, TIA/EIA/IS-95 communication systems typically use common channels. For instance, the base station may use a paging channel to transmit messages to a mobile station, and a mobile station may use an access channel to transmit to the base station. After transmitting a message on the paging channel to the mobile station, the base station would receive the mobile station""s response on the access channel. After transmitting a message on the access channel to the base station, the mobile station would receive the base station""s response on the paging channel. There may be many paging and access channels. The paging channels are distinguished from each other by Walsh codes, and the access channels by long PN (Pseudo-Noise) codes. Different long code masks are used to assign the different long PN codes to the respective access channels.
FIG. 1A illustrates a long code generator in the IS-95 communication system and FIG. 1B shows the long code masks that are assigned to the access channels.
To transmit a message to the base station, the mobile station selects any channel, sets the appropriate transmission power, transmits the message, and waits for a response from the base station. If another mobile station selects the same channel at the same time, the two messages will contend for the same channel and the base station may not receive the message. After no response message is received for a predetermined time period, the mobile station retransmits the message with a higher transmission power than before and waits again for a response message transmitted from the base station.
On a traffic channel, if at least two base stations pick up a signal transmitted by a mobile station, that signal can be effectively received using the diversity effect. On the access channel, even if at least two base stations pick up the same signal, it is difficult for the base stations to know whether the signal is transmitted from the same user or from different users.
In the IS-95 communication system, if one cell is divided into a plurality of sectors, the respective sectors use different spread sequences, each with its own PN offset. However, it is still difficult to know whether the same signal picked up on one access channel by antennas in different sectors is transmitted from the same user or from different users.
FIG. 2 illustrates this problem. One base station is divided into three sectors xcex1, xcex2 and xcex3. If 1ST USER and 2ND USER simultaneously transmit signals on the same access channel R_ACH1, the xcex1 sector antenna can pick up the access channel signal transmitted from the first user and a xcex2 sector antenna can pick up the access channel signal transmitted from the second user. If the base station receiver combines the signals received through the two antennas, it is impossible to receive these signals because of the interference between them. Thus, this contention phenomenon causes difficulty when applying a diversity technique to the access channel at the base station.
It is, therefore, an object of the present invention to provide a device and method by which a base station can combine common channel signals transmitted from a mobile station by a diversity technique in a CDMA communication system.
It is another object of the present invention to provide a device and method by which a base station designates an access channel for a mobile station, and a plurality of base stations receive signals on that access channel to raise the probability of successfully receiving the signals on the access channel in a CDMA communication system.
To achieve these and other objects of the present invention, there is provided a method for diversity combining signals on a common channel in a CDMA communication system, including the steps of:
1) assigning, at a first base station, a dedicated common channel to a mobile station;
2) transmitting, at said first base station, information about the assigned dedicated common channel to a base station controller coupled to said first base station; and
3) transmitting, at said base station controller, said information to at least one second base station which is connected to said base station controller and adjacent to said first base station.